U.S. patent application number 12/312755 was filed with the patent office on 2011-11-03 for quartz encapsulated heater assembly.
Invention is credited to Toshiki Ebata, Kensuke Fujimura, Takeshi Higuchi, Akira Miyahara, Sridhar R. Prasad, Ajay Rao, Eric Witenberter.
Application Number | 20110266274 12/312755 |
Document ID | / |
Family ID | 39284165 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110266274 |
Kind Code |
A1 |
Ebata; Toshiki ; et
al. |
November 3, 2011 |
QUARTZ ENCAPSULATED HEATER ASSEMBLY
Abstract
The current invention relates to a semiconductor wafer heater
assembly having a frosted clear quartz material for the wafer
susceptor (6) that is placed between the heater (8) and the wafer
(7) such that at certain wavelengths of the emitted radiant energy
from the heater (8), the frosted clear quartz material is
`thermally transmissive` to the thermal radiation from the infrared
region. The heater assembly is characterized in that the top quartz
plate or susceptor (6) on which the wafer (7) is supported is made
of a material that is not "optically transmissive" but is more than
90% "thermally transmissive" to infrared emission that is shorter
than 3.5 micrometer wavelength and having higher tolerance and
mechanical strength than conventional clear quartz material.
Inventors: |
Ebata; Toshiki; (Osaka-shi,
JP) ; Prasad; Sridhar R.; (Bangalore, IN) ;
Rao; Ajay; (Bangalore, IN) ; Higuchi; Takeshi;
(Kobe, JP) ; Fujimura; Kensuke; (Kobe, JP)
; Miyahara; Akira; (Ashiya, JP) ; Witenberter;
Eric; (Beachwood, OH) |
Family ID: |
39284165 |
Appl. No.: |
12/312755 |
Filed: |
November 26, 2007 |
PCT Filed: |
November 26, 2007 |
PCT NO: |
PCT/US2007/024432 |
371 Date: |
May 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60867397 |
Nov 27, 2006 |
|
|
|
Current U.S.
Class: |
219/460.1 |
Current CPC
Class: |
H01L 21/67115 20130101;
H05B 3/14 20130101; H01L 21/68757 20130101 |
Class at
Publication: |
219/460.1 |
International
Class: |
H05B 3/68 20060101
H05B003/68 |
Claims
1. A heater assembly comprising a heating element to heat a wafer
to temperatures of at least 700 Degrees C., at least one terminal
and wire to feed electrical power to the heater, a thermal
insulating plate beneath the heater, at least one feed through hole
for the electrical wire and at least one thermo-couple connection,
and a quartz casing to encapsulate said components, said quartz
casing having a top plate positioned between the heating element
and the wafer, wherein said plate comprises a material that is not
optically transmissive and is more than 50 percent thermally
transmissive to an infrared emission that is shorter than 3.5
micron wavelength.
2. The heater assembly of claim 1, wherein the top plate comprises
frosted clear quartz.
3. The heater assembly of claim 2, wherein the frosted clear quartz
has thermal transmissivity of at least 80 percent.
4. The heater assembly of claim 2, wherein the frosted clear quartz
has thermal transmissivity of at least 90 percent.
5. The heater assembly of claim 1, wherein all the components
inside the quartz casing are completely isolated from the chamber
environment by sealing the top plate and quartz casing by
bonding.
6. The heater assembly of claim 1, wherein the top plate is made of
frosted clear quartz and fusion bonded to the quartz casing.
7. The heater assembly of claim 1, wherein the quartz casing other
than the top plate is prepared from clear quartz.
8. The heater assembly of claim 1, wherein the top plate is more
than 50 percent thermally transmissive to an infrared emission that
is shorter than 3.2 micron wavelength.
9. The heater assembly of claim 1, wherein the top plate is more
than 80 percent thermally transmissive to an infrared emission that
is shorter than 3.2 micron wavelength.
10. The heater assembly of claim 1, wherein the top plate is more
than 90 percent thermally transmissive to an infrared emission that
is shorter than 3.2 micron wavelength.
11. A semiconductor processing chamber comprising the heater
assembly of claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and benefit from U.S.
Patent Application No. 60/867,397, filed on Nov. 27, 2006, the
disclosure of which is incorporated herein by reference.
FIELD OF INVENTION
[0002] The invention relates generally to a heater and a heating
assembly for use in a semiconductor-processing chamber.
BACKGROUND OF THE INVENTION
[0003] Semiconductor Integrated Circuits (IC's) are produced
continuously through a series of processes such as thin-film
processing, pattern formation, lithography, etching & doping on
the surface of a substrate such as a silicon wafer. These IC's can
be produced continuously by intermittently introducing the cleaning
process in-between. For example, in thin film processing, the
deposition process device forms a thin film of the metal and the
insulator on the wafer surface. First, the process device is
completely evacuated and a heating mechanism is installed within it
to heat the silicon wafer to a prescribed temperature. Next, the
necessary reactant gases are introduced within the chamber of this
device. These gases accumulate around the wafer and a thin-film is
formed on the wafer due to the chemical reaction of these gases.
The process is completed when the desired film thickness is
obtained on the wafer and it is then carried away from the device.
In this process, the susceptor (wafer supporting stage) that is
present within this device is heated from around 450 Degrees C. to
650 Degrees C. in vacuum conditions and it is at this high
temperature that the chemical reaction gets initiated.
[0004] In such a process, the surface of the susceptor, or the
heater surface or the wiring section that supplies the electricity
to the heater are already at high temperatures and when they come
in direct contact with the reacting gases it results in chemical
reactions that generate certain impurities and these impurities
then spread inside the chamber of this device, ultimately resulting
in polluting the semiconductor wafer.
[0005] One method of overcoming the above problem involves having
ceramics such as aluminum nitride (AlN) with a heater electrode and
wirings embedded. These ceramic materials are highly resistant to
any corrosion medium or material. But ceramics such as AlN are very
brittle in nature and frequent heating and cooling of these may
result in cracking. Also purity of those ceramics cannot be
perfect, as they typically require a binder when being sintered.
Further, at higher temperatures of operation the electrical
resistance of the ceramic material decreases drastically and this
can result in poor insulation of the heaters.
[0006] Another method to solve this problem is to encapsulate the
heater, susceptor, wiring etc. with a high purity quartz casing.
These components are sealed inside an airtight quartz casing and
later purged by inert gas. This will mitigate the corrosion of
these components by corrosive gases (reactant or cleaning) since
quartz material is highly non-reactive in nature. Till recently,
the susceptor material that was made out of high purity quartz and
were widely used in the silicon wafer thin film processing were
restricted mainly to operating temperatures ranging from 450
Degrees C. to 600 Degrees C. However, with recent advances being
made to improve the efficiency of IC's through Large Scale
Integration (LSI), it has resulted in the requirement of the target
wafer temperature for thin film deposition to be in the range of
800 Degrees C. to 900 Degrees C. Also, in such processes that
involve very high temperatures, it is observed that the operating
temperature of the heater is at least 200 Degrees C. greater than
that of the target wafer temperature. This is due to the presence
of the prior art quartz material in between the heater and the
wafer surface. It is also seen that the temperature of the prior
art quartz material itself in these high temperature applications
exceeds over 1000 Degrees C. It is known that quartz being an
amorphous vitrified structure, its viscosity decreases with
temperature and it has a critical viscous or softening point at
about 1350 Degrees C.
[0007] In other words, the extent by which the temperature of the
prior art quartz exceeds 1000 Degrees C., the higher is the plastic
deformation of the prior art quartz material. In addition, when the
prior art quartz material is cooled down to below 1000 Degrees C.,
strong thermal strain is set-in and this results in the generation
of very high internal stresses within the material. These internal
stresses decrease the overall mechanical strength of the material.
In most applications, the device chamber is maintained under vacuum
conditions whereas the quartz casing that houses the heater and
other components is filled by an inert gas. The pressure
differential between the inside and the outside of the casing made
from the prior art quartz material is usually around 1 atmosphere.
This pressure differential is sufficient enough to break the quartz
casing since now the quartz plate can no longer withstand the
design strength as its strength has been reduced due to the
internal stresses developed within the material. This invariably
leads to the mechanical deformation of the quartz susceptor,
resulting in a poor surface contact between the wafer and the
susceptor and, as such, heating of the wafer through thermal
conduction is no longer efficient. Hence, for achieving the same
wafer temperature, the heater will now need to operate at a much
higher temperature.
[0008] What is needed in the art is a heater assembly having a
susceptor or wafer-supporting stage which when placed between the
heater and the wafer does not have issues related to reliability,
mechanical deformation and damage even at high operating
temperatures and will efficiently heat the semiconductor wafer to
the desired target temperature without generating any
contaminants.
SUMMARY OF THE INVENTION
[0009] According to one embodiment of the invention, a heater
assembly is provided comprising a heating element to heat a wafer
to temperatures of at least 700 Degrees C., at least one terminal
and wire to feed electrical power to the heater, a thermal
insulating plate beneath the heater, at least one feed through hole
for the electrical wire and at least one thermo-couple connection,
and a quartz casing to encapsulate said components, said quartz
casing having a top plate positioned between the heating element
and the wafer, wherein said plate comprises a material that is not
optically transmissive and is more than about 50 percent thermally
transmissive to an infrared emission that is shorter than 3.5
micron wavelength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1(a)-(b) presents the transmissivity of the "thermally
transmissive" frosted clear quartz material for blackbody thermal
radiation at 500 Degrees K and 1500 Degrees K.
[0011] FIG. 2 presents a quartz encapsulated heater assembly in
which the susceptor is made from frosted clear Quartz material.
[0012] FIG. 3 presents a heater assembly used to evaluate the
radiative heating efficiency of the various quartz materials
[0013] FIG. 4 is a graphical representation of the radiative
heating efficiency of Example 1, i.e., Frosted Clear Quartz;
Example 2, i.e., Clear Quartz; and Example 3, i.e., High Density
Opaque (HDO) Quartz.
DETAILED DESCRIPTION OF THE INVENTION
[0014] As used herein, approximating language may be applied to
modify any quantitative representation that may vary without
resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as "about"
and "substantially," may not to be limited to the precise value
specified, in some cases.
[0015] Also as used herein, the "heating apparatus," may be used
interchangeably with "treating apparatus," "heater," "electrostatic
chuck," "chuck," or "processing apparatus," referring to an
apparatus containing at least one heating and/or cooling element to
regulate the temperature of the substrate supported thereon,
specifically, by heating or cooling the substrate.
[0016] As used herein, the term "substrate" refers to the
semiconductor wafer or the glass mold being supported/heated by the
processing apparatus of the invention. As used herein, the term
"sheet" may be used interchangeably with "layer."
[0017] As used herein, the term "circuit" may be used
interchangeably with "electrode," and the term "heating element"
may be used interchangeably with "heating electrode," "electrode,"
"resistor," "heating resistor," or "heater." The term "circuit" may
be used in either the single or plural form, denoting that at least
one unit is present.
[0018] The current invention relates to a heater assembly having a
new quartz material, i.e., frosted glass quartz, for the wafer
susceptor that is placed between the heater and the wafer such that
at certain wavelengths of the emitted radiant energy, either in a
scattered transmission or direct transmission mode, from the heater
this quartz material is "thermally transmissive" to the thermal
radiation from the Infrared region (IR). According to one
embodiment of the invention the frosted glass quartz is thermally
transmissive to at least 50 percent of the IR emission that is
shorter than 3.5 micron-meters. According to another embodiment of
the invention the frosted glass quartz is thermally transmissive to
at least 80 percent of the IR emission that is shorter than 3.5
micron-meters. According to another embodiment of the invention the
frosted glass quartz is thermally transmissive to at least 90
percent of the IR emission that is shorter than 3.5
micron-meters.
[0019] Frosted clear quartz is defined herein as a quartz material
with a roughened surface, the surface roughening being of the
dimensions such that it would scatter at least 20 percent, and
preferably 50 percent of the visible light. As such, the frosted
clear quartz is not optically transmissive. Frosted clear quartz
can be prepared, for example, by sandblasting the surface of clear
quartz.
[0020] In one aspect, the invention relates to a
quartz-encapsulated heater, at temperatures higher than 700
Degrees, as the peak of the infrared (IR) emission spectrum from
the heater starts shifting towards shorter wavelengths, majority of
the IR emission begins to completely transmit through the susceptor
which is made of frosted clear quartz material. This is due to the
fact that frosted clear quartz susceptor is "thermally
transmissive" to the IR emission that is shorter than 3.5
micron-meters and hence most of the emission passes through the
frosted clear quartz susceptor directly to the Si wafer. Thus,
heating the wafer through the frosted clear quartz susceptor is
equivalent to heating the wafer directly without a top plate
(susceptor), for example, there is a 10 Degree C. difference
between heating a wafer through the frosted clear quartz susceptor
and heating a wafer directly without a top plate at 900 degrees
C.
[0021] Additionally, it is contemplated herein that the frosted
clear quartz surface acts to some extent as an "anti-reflection
coating/surface" which reduces the amount of IR light that is being
reflected back to the heater. In this regard, the frosted clear
quartz provides superior heating effects when compared to clear
quartz and other types of quartz materials.
[0022] The current invention relates to a heater assembly having a
frosted clear quartz material for the wafer susceptor that is
placed between the heater and the wafer such that at certain
wavelengths of the emitted radiant energy from the heater, the
frosted clear quartz material is "thermally transmissive" to the
thermal radiation from the Infrared region. The desired wafer
temperature can now be achieved at almost the same heater
temperature as direct heating of the wafer by the heater.
Additionally, the presence of the frosted clear quartz top plate
prevents the contamination of the heater without compromising the
radiative heating efficiency. Also, the frosted clear quartz
material possesses better tolerance and mechanical strength than
conventional clear quartz material.
[0023] FIGS. 1a and 1b show the relationship between the blackbody
spectrum of the object that is heated and the transmissivity of
frosted clear quartz for 500 degrees K and 1500 degrees K. Such a
quartz material that is so transparent to thermal radiation is
normally termed as "thermally transmissive" quartz. From the figure
we can conclude that at higher temperatures, the spectrum of the
blackbody radiant energy shifts towards the shorter wavelength
regime. At 500 degrees K, this "thermally transmissive" quartz does
not transmit most of the thermal radiation and is thus sufficiently
heated. However, at higher temperatures such as 1500 degrees K,
most of the radiant energy gets transmitted through the "thermally
transmissive" quartz material. High wafer temperature, i.e., wafer
temperatures greater than 700 degrees C. can now be achieved at
almost the same heater temperature as direct heating of the wafer
by the heater. Importantly, the presence of the frosted clear
quartz top plate prevents the contamination of the heater without
compromising the radiative heating efficiency. As such, improved
efficiency of the radiant energy from the heater to the silicon
wafer is obtained when the top quartz plate or the susceptor on
which the wafer is supported is made of a material that is at least
50 percent, and preferably more than 90 percent "thermally
transmissive" to infrared emission having a wavelength that is
shorter than 3.5 micron.
[0024] According to one embodiment of the invention, the heater
assembly is encapsulated with a top plate quartz or susceptor made
out of frosted clear quartz of the present invention. Whereas the
lower parts of the quartz casing are made from clear quartz, i.e.,
quartz material possessing a transparency to visible light of
greater than about 80 percent, and the entire casing is made
airtight by using techniques known in the art.
[0025] In one specific embodiment of the invention, as presented in
FIG. 2, the heater assembly comprises a heater 8, radiation shield
9, heater power supplies 11 and 12 and thermocouple 13 all of which
are encapsulated with a top plate or susceptor 6 made out of
frosted clear quartz. The lower parts of the quartz casing 10 are
made from clear quartz and the entire quartz casing 10 can be made
air-tight by techniques known in the art, e.g., bonding.
[0026] Examples of a heater assembly with various quartz plates
(i.e., Example 1 and Comparative Examples 2 and 3) were prepared to
evaluate their radiative heating efficiency. The heater assembly
consisted of three main components: A Radiative Heat Source
(Pyrolytic Boron Nitride (PBN) Ceramic Heater), A Receiver (an
inverted graphite cover) and the quartz plate placed is between the
heat source and the receiver.
[0027] The quartz plate placed between the radiative heater and the
graphite receiver in Example 1 is Frosted Clear Quartz, the quartz
plate in Comparative Example 2 is Clear Quartz, and in Comparative
Example 3 the quartz plate is High Density Opaque (HDO) Quartz,
i.e., quartz material having a transparency to visible light of
less than about 50 percent, and in most cases a transparency to
visible light of less than 20 percent. The heater assembly also
consisted of 4 temperature measurement thermocouples. These
thermocouples were embedded in specific positions such that they
measure the temperature of: the radiant heater, the quartz slab,
i.e., quartz plate, the inverted graphite cover center, edge and
sidewall. The heater assembly along with a description of the
various components and the thermocouple locations is presented in
FIG. 3.
[0028] Table 1 presents data for Example 1 and Comparative Examples
2 and 3. For a fixed heater temperature, the temperature at the
center of the inverted graphite cover is the highest when the
quartz plate between the heater and the receiver is made of frosted
clear quartz. As represented by the data presented in Table 1 the
radiative heating efficiency (highest to lowest) is as follows:
Frosted Clear Quartz, Clear Quartz, HDO Quartz.
[0029] FIG. 4 is a graphically representation of the radiative
heating efficiency of the materials of Example 1 (Frosted Clear
Quartz), Comparative Example 2 (Clear Quartz), and Comparative
Example 3 (High Density Opaque (HDO) Quartz). Based on the data
presented in FIG. 4, it can be noted that to achieve a fixed wafer
temperature the required heater temperature is lower when the top
plate is made of either frosted clear quartz or clear quartz as
compared to HDO quartz. Additionally, the better tolerance and
mechanical strength of frosted clear quartz makes it a more
suitable material for the outer quartz casing.
[0030] Table 1 presents the experimental data of Example ! and
Comparative examples 2 and 3. Temperature in Centigrade (TC).
TABLE-US-00001 (Ex. 1) (CompEx 2) (CompEx 3) Example 1 Comp. Ex. 2
Comp. Ex. 3 Graphite Cover Graphite Cover Graphite Cover Heater TC
Frosted Quartz TC Clear Quartz TC HDO Quartz TC TC (Frosted) TC
(Clear) TC (HDO) 400.0 340.8 335.8 343.4 204.5 191.3 192.1 600.0
530.0 525.8 528.7 371.4 351.4 339.6 800.0 715.9 712.5 707.0 536.6
521.0 492.9 1000.0 912.0 905.9 889.7 701.1 692.7 643.7 1200.0
1112.9 1088.2 1091.2 835.3 825.4 791.7
[0031] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to make and use the invention. The patentable
scope of the invention is defined by the claims, and may include
other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they
have structural elements that do not differ from the literal
language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal languages
of the claims. All citations referred herein are expressly
incorporated herein by reference.
* * * * *